Conventionally, in order to improve the efficiency of fishing, fishermen fish at a location (e.g., a fish reef or a shallow) where many target fish are considered to inhabit. The fishermen operate a ship so that a heading opposes to the direction of wind, so as to confirm whether the target fish exist at the location (so-called drift fishing).
In order to carry out the drift fishing, the ship needs to be attached with a spanker for orienting a bow in the direction of wind (see Patent Document 1.) or a side thruster for moving in a desired direction (e.g., in a starboard/port direction of a ship) (see Patent Document 2.).